Si–N Heterodehydrocoupling with a Lanthanide Compound

[La­{N­(SiMe₃)₂}₃THF₂] (<b>1</b>) is an effective precatalyst for the heterodehydrocoupling of silanes and amines. Coupling of primary and secondary amines with aryl silanes was achieved with a loading of 0.8 mol % of [La­{N­(SiMe₃)₂}₃THF₂]. With primary amines, generation of tertiary and sometimes quaternary silamines was facile, often requiring only a few hours to reach completion, including new silamines Ph₃Si­(^<i>n</i>PrNH) and Ph₃Si­(^<i>i</i>PrNH). Secondary amines were also available for heterodehydrocoupling, though they generally required longer reaction times and, in some instances, higher reaction temperatures. This work expands upon the utility of <i>f</i>-block complexes in heterodehydrocoupling catalysis

Zirconium-Catalyzed Intermolecular Double Hydrophosphination of Alkynes with a Primary Phosphine

Catalytic double hydrophosphination of internal alkynes and primary phosphines is possible using a zirconium complex, [κ⁵<i>-N,N,N,N,C</i>-(Me₃SiNCH₂CH₂)₂NCH₂CH₂NSiMe₂CH]Zr (<b>1</b>). The reaction proceeds via stepwise hydrophosphination to give vinyl phosphine products, which can be isolated or further converted to the respective 1,2-bis­(phosphino)­ethane (i.e., double hydrophosphination). The catalysis is highly selective for formation of secondary phosphine products

Iridium Pincer Catalysts for Silane Dehydrocoupling: Ligand Effects on Selectivity and Activity

Catalytic reactions of bisphosphinite pincer-ligated iridium compounds <i>p</i>-X^<i>R</i>(POCOP)­IrHCl (POCOP) [2,6-(R₂PO)₂C₆H₃, R = ^<i>i</i>Pr, X = H (<b>1</b>); R = ^<i>t</i>Bu, X = COOMe (<b>2</b>); = H (<b>3</b>); = NMe₂ (<b>4</b>)] with primary and secondary silanes have been performed. Complex <b>1</b> is primarily a silane redistribution precatalyst, but dehydrocoupling catalysis is observed for sterically demanding silane substrates or with aggressive removal of H₂. The bulkier compounds (<b>2</b>–<b>4</b>) are silane dehydrocoupling precatalysts that also undergo competitive redistribution with less hindered substrates. Products generated from reactions utilizing <b>2</b>–<b>4</b> include low molecular weight oligosilanes with varying degrees of redistribution present or disilanes when employing more sterically demanding silane substrates. Selectivity for redistribution versus dehydrocoupling depends on the steric and electronic environment of the metal but can also be affected by reaction conditions

Iridium Pincer Catalysts for Silane Dehydrocoupling: Ligand Effects on Selectivity and Activity

Catalytic reactions of bisphosphinite pincer-ligated iridium compounds <i>p</i>-X^<i>R</i>(POCOP)­IrHCl (POCOP) [2,6-(R₂PO)₂C₆H₃, R = ^<i>i</i>Pr, X = H (<b>1</b>); R = ^<i>t</i>Bu, X = COOMe (<b>2</b>); = H (<b>3</b>); = NMe₂ (<b>4</b>)] with primary and secondary silanes have been performed. Complex <b>1</b> is primarily a silane redistribution precatalyst, but dehydrocoupling catalysis is observed for sterically demanding silane substrates or with aggressive removal of H₂. The bulkier compounds (<b>2</b>–<b>4</b>) are silane dehydrocoupling precatalysts that also undergo competitive redistribution with less hindered substrates. Products generated from reactions utilizing <b>2</b>–<b>4</b> include low molecular weight oligosilanes with varying degrees of redistribution present or disilanes when employing more sterically demanding silane substrates. Selectivity for redistribution versus dehydrocoupling depends on the steric and electronic environment of the metal but can also be affected by reaction conditions

Intermolecular Zirconium-Catalyzed Hydrophosphination of Alkenes and Dienes with Primary Phosphines

Catalytic hydrophosphination of terminal alkenes and dienes with primary phosphines (RPH₂; R = Cy, Ph) under mild conditions has been demonstrated using a zirconium complex, [κ⁵-<i>N</i>,<i>N</i>,<i>N</i>,<i>N</i>,<i>C</i>-(Me₃SiN­CH₂CH₂)₂­NCH₂CH₂­NSiMe₂­CH]Zr (<b>1</b>). Exclusively anti-Markovnikov functionalized products were observed, and the catalysis is selective for either the secondary or tertiary phosphine (i.e., double hydrophosphination) products, depending on reaction conditions. The utility of the secondary phosphine products as substrates for further elaboration was demonstrated with a platinum-catalyzed asymmetric alkylation reaction

Visible Light Photocatalysis Using a Commercially Available Iron Compound

[CpFe­(CO)₂]₂ (<b>1</b>) (Cp = η⁵-C₅H₅) is an effective precatalyst for the hydrophosphination of alkenes with Ph₂PH under visible light irradiation, which appears to be a unique way to promote metal-catalyzed hydrophosphination. Additionally, <b>1</b> is a photocatalyst for the dehydrogenation of amine boranes and formation of siloxanes from tertiary silanes. These reactions have similar, if not improved, reactivity over the same transformations using <b>1</b> or related CpFeMe­(CO)₂ under UV irradiation, consistent with the notion that hydrophosphination with <b>1</b> proceeds via formation of CpFe­(CO)₂^•. These results demonstrate that catalyst selection can avail the use of commercially available LED bulbs as photon sources, potentially replacing mercury arc lamps or other energy intensive processes in known or new catalytic reactions

Zirconium-Catalyzed Amine Borane Dehydrocoupling and Transfer Hydrogenation

κ⁵-(Me₃SiNCH₂CH₂)₂N­(CH₂CH₂NSiMe₂CH₂)Zr (<b>1</b>) has been found to dehydrocouple amine borane substrates, RR′NHBH₃ (R = R′ = Me; R = ^<i>t</i>Bu, R′ = H; R = R′ = H), at low to moderate catalyst loadings (0.5–5 mol %) and good to excellent conversions, forming mainly borazine and borazane products. Other zirconium catalysts, (N₃N)­ZrX [(N₃N) = N­(CH₂CH₂NSiMe₂CH₂)₃, X = NMe₂ (<b>2</b>), Cl (<b>3</b>), and O^<i>t</i>Bu (<b>4</b>)], were found to exhibit comparable activities to that of <b>1</b>. Compound <b>1</b> reacts with Me₂NHBH₃ to give (N₃N)­Zr­(NMe₂BH₃) (<b>5</b>), which was structurally characterized and features an η² B–H σ-bond amido borane ligand. Because <b>5</b> is unstable with respect to borane loss to form <b>2</b>, rather than β-hydrogen elimination, and <b>2</b>–<b>4</b> do not exhibit X ligand loss during catalysis, dehydrogenation is hypothesized to proceed <i>via</i> an outer-sphere-type mechanism. This proposal is supported by the catalytic hydrogenation of alkenes by <b>2</b> using amine boranes as the sacrificial source of hydrogen

As–As Bond Formation via Reductive Elimination from a Zirconocene Bis(dimesitylarsenide) Compound

A new zirconocene bis­(arsenide) derivative, Cp₂Zr­(AsMes₂)₂ (<b>1</b>; Cp = cyclopentadienyl, Mes = 2,4,6-trimethylphenyl), has been prepared by the metathetical reaction of 2 equiv of LiAsMes₂ with Cp₂ZrCl₂ and structurally characterized. Efforts to prepare Cp₂ZrCl­(AsMes₂) (<b>2</b>) by reaction of 1 equiv of LiAsMes₂ with Cp₂ZrCl₂ yielded a mixture of products that could not be separated, including <b>1</b> and <b>2</b>, as identified by ¹H NMR spectroscopy. Compound <b>1</b> thermally decomposes with formation of As₂Mes₄, suggestive of reductive elimination to form an As–As bond. Further evidence for reductive elimination comes from effective interception of a putative zirconium­(II) intermediate with diphenylacetylene to give Cp₂Zr­(C₄Ph₄)

As–As Bond Formation via Reductive Elimination from a Zirconocene Bis(dimesitylarsenide) Compound

A new zirconocene bis­(arsenide) derivative, Cp₂Zr­(AsMes₂)₂ (<b>1</b>; Cp = cyclopentadienyl, Mes = 2,4,6-trimethylphenyl), has been prepared by the metathetical reaction of 2 equiv of LiAsMes₂ with Cp₂ZrCl₂ and structurally characterized. Efforts to prepare Cp₂ZrCl­(AsMes₂) (<b>2</b>) by reaction of 1 equiv of LiAsMes₂ with Cp₂ZrCl₂ yielded a mixture of products that could not be separated, including <b>1</b> and <b>2</b>, as identified by ¹H NMR spectroscopy. Compound <b>1</b> thermally decomposes with formation of As₂Mes₄, suggestive of reductive elimination to form an As–As bond. Further evidence for reductive elimination comes from effective interception of a putative zirconium­(II) intermediate with diphenylacetylene to give Cp₂Zr­(C₄Ph₄)

As–As Bond Formation via Reductive Elimination from a Zirconocene Bis(dimesitylarsenide) Compound

A new zirconocene bis­(arsenide) derivative, Cp₂Zr­(AsMes₂)₂ (<b>1</b>; Cp = cyclopentadienyl, Mes = 2,4,6-trimethylphenyl), has been prepared by the metathetical reaction of 2 equiv of LiAsMes₂ with Cp₂ZrCl₂ and structurally characterized. Efforts to prepare Cp₂ZrCl­(AsMes₂) (<b>2</b>) by reaction of 1 equiv of LiAsMes₂ with Cp₂ZrCl₂ yielded a mixture of products that could not be separated, including <b>1</b> and <b>2</b>, as identified by ¹H NMR spectroscopy. Compound <b>1</b> thermally decomposes with formation of As₂Mes₄, suggestive of reductive elimination to form an As–As bond. Further evidence for reductive elimination comes from effective interception of a putative zirconium­(II) intermediate with diphenylacetylene to give Cp₂Zr­(C₄Ph₄)